An oil well is a hole bored through layers of rock formations to reach a level or bed of petroleum or gas. The desired petroleum or gas is often found at a depth as deep as 25,000 feet to 30,000 feet. After the initial bore hole is drilled with a drilling rig, a casing is run into the bore hole and cemented to the sides of the bore hole to keep the bore hole from collapsing.
If a casing is provided along the entire length of the borehole, the casing is perforated at the proper level to permit the top of the petroleum or gas to enter the casing for recovery. The casing may be run into the bore hole down to the hydrocarbon producing formation. This technique is referred to as open hole completion. The portion of the bore hole below the deposit is then unprotected from collapsing.
Almost all of the gas or oil wells drilled require some type of treatment to render the well productive. This often includes the pumping of acid; or acid and different sizes and grades of salt; or sand pumped under high pressure to fracture the formation in the oil or gas bearing layer. When the treatment is completed, some debris, formed by the acid, sand, salt or other material, is left in the bore hole. This commonly leads to closing the hydrocarbon or gas producing formations to stop recovery.
Several techniques have been developed to remove debris from within a bore hole. A reverse unit may be employed which includes a rotary device above the oil or gas bore hole to turn a drill pipe or tubing. The drill pipe or tubing has a drill bit on the bottom end thereof and is run down into the bore hole to drill through the debris for cleaning or cleaning by drilling the well deeper. The reverse unit includes a pump on the surface at the bore hole for pumping fluid down hole to recover the debris and pump it to the surface. However, this technique is not always possible. Sometimes, cleaning or drilling circulation is impossible. In other instances, fluid may not be placed in gas wells as it will push the gas back into the formation and prevent little, if any, recovery of the gas.
To overcome this problem, several wire line clean-out tools have been developed. The tools are placed down hole on a wire line or cable suspended from the surface. The wire line tools basically operate on two principals, either hydraulic or hydrostatic. A hydraulic device is disclosed in U.S. Pat. No. 4,190,113 to Harrison issued Feb. 26, 1980. This type of device operates by alternately evacuating and pressurizing a debris chamber with a pumping unit activated by the wire line. A one-way valve entering the debris chamber from the bore hole permits debris to flow into the debris container when the container chamber is evacuated. The debris is blocked from flowing out of the borehole by the valve when the chamber is pressurized. The pumping assembly is operated until the debris container chamber is full of debris. The tool is then removed and cleaned for reuse.
Fluid pumped by the pumping assembly is discharged horizontally from ports in the device into the narrow annular space between the device and borehole. This inhibits fluid motion downward in this annular space past these ports. In another device disclosed in this patent, a tubing string extends to the surface above the debris chamber. A kelly permits rotation of a notched collar below the chamber through the tubing string to break debris crust in the well bore. The presence of an empty tubing string in the well bore raises the potential for tubing collapse if the hydrostatic pressure in the well bore acting on the walls of the tubing string becomes to large.
The previously known hydraulic types of tools have several shortcomings. The vacuum within the chamber is limited and heavy or large debris will not be recovered. The pumping action also permits the tool to become submerged within the debris and possibly be incapable of recovery by the wire line. An extremely costly and time consuming fishing job is then required to get the tool from the well.
U.S. Pat. Nos. 3,406,757, 3,446,283 and 3,651,867, issued on Oct. 11, 1968, May 27, 1969 and Mar. 28, 1972, respectively describe hydrostatic tools. Each of these patents is issued to Baumstimler. In a hydrostatic tool, the tool is run down the bore hole with a sealed debris chamber at atmospheric pressure. The tool is set down on top of the debris in the well. A valve is then opened permitting the fluid in the bore hole to enter the debris chamber. With sufficient fluid in the bore hole, the hydrostatic head is much greater than the atmospheric pressure within the debris chamber and the inrush of fluid entrains debris into the debris chamber. The tool must then be lifted from the bore hole to remove the debris in the debris chamber.
The hydrostatic tool also suffers shortcomings. The hydrostatic head in the bore hole where the debris is located must be relatively high to permit satisfactory operation of the hydrostatic tool. It is quite expensive to add sufficient fluid to the bore hole to achieve this hydrostatic head if it is not provided naturally. When the well is returned to production, the fluid has to be recovered and disposed of at additional cost. While the hydrostatic tool is effective on large and heavy debris, there is little control of how much the debris containing chamber will contain. Prior known tools provide little control of fluid motion once the debris chamber is exposed to the bore hole pressures and the hydrostatic tool can easily become submerged within the debris and require a fishing operation for removal.
A need exists for a tool which may be employed as either a hydraulic or hydrostatic tool without major modifications to achieve the advantages of either tool operation in a particular application. A need also exists to develop a tool with a capacity to provide sufficient forces to lift the tool in either mode of operation from within the debris in the bore hole. U.S. Pat. No. 2,992,682 issued July 18, 1961 to Yates discloses a combination tool operable in both the hydrostatic and hydraulic mode. However, this tool is not readily transferrable from one mode of operation to the other and still retains the shortcoming of other known tools in failing to provide an effective technique for removing the tool from the bore hole when buried in debris.